The present invention relates to cooling technology for a nuclear reactor. More specifically, especially preferred embodiments of the invention relate to cooling apparatus and techniques suitable for use in removing the decay heat from a reactor container, which decay heat is produced in a reactor core at the time of a loss of coolant (LOCA) accident.
Japanese patent publication No. 63-191096 (1988) discloses an arrangement which includes a cooling water pool around the outer periphery of a nuclear reactor container with transfer of heat from a pressure suppression chamber in the reactor container to the outer water pool through a heat conducting surface of the container according to a temperature difference therebetween, by means of the natural convection both in the pressure suppression chamber and the outer pool. Eventually the heat is removed by evaporation of the pool water. Further, an air-conditioning system is normally in operation to cool an internal heat and remove it from the reactor container.
An upper space of the reactor container is purged with a nitrogen gas in normal operations. According to the prior art set forth in the above publication, as only the gas present in the vicinity of the inner surface of the reactor container is capable of being cooled, there is a problem that the gas in the center portion is not likely to be cooled, failing to attain an efficient heat removal. Further, there is a problem that conventional air-conditioning systems normally provided therein are not capable of coping with an emergency or accident because of their insufficient handling capacities.
An object of the present invention is to provide a nuclear reactor and nuclear reactor cooling facilities, a nuclear power generation plant and a method of its operation, wherein reliability in cooling functions at the time of emergencies is substantially improved by enhancing the cooling efficiency for the gas in the reactor container.
A second object of the present invention is to provide a nuclear reactor and nuclear reactor cooling facilities, a nuclear power generation plant and a method of its operation wherein reliability in cooling functions at the time of emergencies is substantially improved, without resorting to any active external power source.
The above-noted first object is achieved according to preferred embodiments of the invention by providing means for circulating the gas in the reactor container so as to accelerate heat removal out of the reactor container therethrough. More specifically, the accelerated heat removal is accomplished by providing an arrangement including internal structure for retaining the coolant in the reactor container, an upper space disposed over the internal structure, a first gas passage for directing the gas in the upper space downward, and a second gas passage connecting between the first gas passage and the upper space.
The above-noted second object of the present invention is accomplished by providing means for circulating the gas in the reactor container by utilizing a decay heat therein.
By circulating the gas in the reactor container, a gas present in the center potion thereof is also capable of being directed toward the vicinity of the inner surface of the reactor container. As a result, heat existing in the center portion is also capable of being removed from the reactor container therethrough.
Further, in a nuclear reactor the reactor container of which is partitioned by an inner structure and an upper space thereabove, retention of a gas in the upper space is prevented according to preferred embodiments of the invention by once directing the upper space gas downward, and then recirculating the same gas upward to the upper space. With this arrangement, heat in the upper space is removed rather readily on the whole through the reactor container. A preferred route for the gas to be directed downward is along the inner surface of the reactor container. Far more enhanced heat removal effect will be achieved by cooling the outer surface of the reactor container with air or the like according to especially preferred embodiments.
In order to circulate the gas, some appropriate means for this purpose is provided by preferred embodiments of the invention. Hence, by providing means for permitting the gas which was directed downward cooled along the inner surface of the reactor core to be directed upward by utilizing a decay heat generated at the time of an accident, so-called natural circulation for recirculating the gas is accomplished without utilizing any particular external power source. For example, in a nuclear reactor having a pressure suppression chamber retaining cooling water to condense a discharge gas from the reactor container, a natural circulation is capable of being implemented by permitting the cooled gas which came down condensed along the inner surface of the container to be carried upward by the vapor generated in the pressure suppression chamber.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.